In a manufacturing process of LED devices, in order to improve the light extraction efficiency from the devices to the outside, it is practiced to execute etching process (plasma processing) as a step for forming a minor concavo-convex structure on a surface of a sapphire substrate. In such etching process, a plurality of substrates are treated as they are received by a tray (see, e.g., Patent Literature 1).
More specifically, a plurality of substrate receiving holes are formed in the tray, and an edge portion of each sapphire substrate is supported by a substrate support portion projected from an inner wall of each substrate receiving hole, thus allowing a plurality of substrates to be received by the tray. A substrate stage is placed in a chamber of the plasma processing apparatus, and a tray support portion and a plurality of substrate holding portions projecting upward from the tray support portion are provided on the top face of the substrate stage.
For execution of the etching process, a plurality of substrates are carried into the chamber as they are received by the tray, and the tray is placed on the tray support portion, so that the plurality of substrates are placed on the substrate holding portions, respectively, while edge portions of the substrates are set apart from the substrate support portions. In such a state, the individual substrates are electrostatically absorbed by ESCs (Electro-Static Chucks) contained in the substrate holding portions, and the etching process on the substrates is executed while the substrates are held by the substrate holding portions. Upon completion of the etching process, the absorption and holding by the ESCs is released, and the tray is lifted from the tray support portion while the edge portions of the substrates are supported again by the substrate support portions, in which state a plurality of substrates are carried out from within the chamber.